Stabilization of cellulose xanthate



Patented Sept. 27, 1932 I "FICE GEORGE A. RICHTER AND PHILIP C. SCHERER, JR., 0E BERLIN, NEW HAMPSHIRE, AS- SIGNORS TO BROWN COMPANY,OF BERLIN, vNERT HAMPSHIRE, A CORPORATION OF MAINE STABILIZATION OF CELLULOSE IXANTHATE No Drawing.

The aged product is treated with sufficient carbon 'bisulphide to effect xanthation, the resulting cellulose xanthate being an orangecolored product which is soluble in a solution of alkali to produce a solution or syru which is known as viscose and which may e spun into artificial silk or used in making films or as a size for textiles or the like.

Cellulose xanthate produced as hereinbefore described is quite unstable while in the moist condition, sulphur groups progressively splitting off to form complexes containing a higher percentage of cellulose than the xanthate, so that when spontaneous decomposition is allowed to proceed, a substantially complete regeneration of the cellulose may take place.

' In the past, attempts at stabilization of cellulose xanthate have not succeeded owing to the failure to reco ize that this spontaneous and progressive ecomposition is largely caused by hydrolysis in the sense of the following equations:

(C H OQXCS Na HOH= c,H.o, ,cs H NaOH cellulose xanthate cellulose xanthic acid a i 5) 2 l HOH: 6 m05) H28 C03 cellulose Thus, any process which will tend to repress hydrolysis will tend to stabilize the cellulose xanthate. We have found that gelling of viscose solution may be prevented for cor.-

siderably longer than normal by adding to the solution products of the hydrolysis and' thus repressing such h drolysis. We have further found that the simplest way in which to prevent hydrolysis is to remove all mois- 5 ture, uponwhich, decomposition caused by hydrolysis. becomes impossible, if the bone- App1ication filed October 15,1928. Serial No. 312,747.

dry product is kept from contact with moistureor the atmosphere until used. Removal of moisture from cellulose xanthate may be accomplished in any of the customary ways of'removing moisture, but we have found that the best results are obtained if that removal is carried out very tures. If high temperatures and long periods of dehydration are used, decomposition of cellulose xanthate may ensue before dehydration is complete.

I The object of the present invention is to effect a suflicient stabilization of cellulose xanthate so that it may be kept for a considerable period without undergoing material decomposition We have found that this object may be attained by dehydrating the xanthate, providing that this dehydration is carried out as rapidly and at as low a temperature as possible, as 'hereinbefore described. The dehydrated product so obtained may be preserved indefinitely, provided it is kept out of contact with moisture. A further way of preservingthe product is by grinding it to comparatively small particle size, and coating the particles with a water-repellent material, preferably one which is soluble in a solution of alkali, so that the stabilized xanthate may be dissolved as usual to form viscose. We have also found that the stability of the xanthate may be further increased and a lower viscosity viscose obtainedif impurities are removed from the xanthate' before its dehydration.

The purification of the cellulose xanthate may be effected immediately after xanthation, that is, while in'the form of a mass of crumbs, as by treating with a mixture of acetic acid and alcohol or othersuitable reagent which efiects a removal of secondary rapidly and at low temperareactionproducts and excess caustic soda, the

color of the xanthate changing to light yellow while the reagent assumes a dark orange or brown color. ,The xanthate is then pressed free of excess reagent and dried, preferably under vacuum conditions and at a comparatively low temperature, say 20 to 30 0.,

under which conditions dehydrat1on is ragidly accomplished. .Or the xanthate may purifiedby dissolving in a solution of alkali and then precipitating the xanthate from solution by the addition of a suitable precipitant, such as acetic acid, alcohol, or ammonium chloride solution -or by delivering the solution of xanthate t rough a s inneret into a precipitatin bath in thin ri bon or filament form. The resulting flocculent precipitate or continuous ribbon or filament of cellulose xanthate may be washed, dehydrated, and pulverized.

A better appreciation of the present-invention may be had from the followingspecific example of procedure which was ound to give satisfactory results in actual practice, starting with ange-colored xanthated crumbs of fiber usually obtained, purified xanthate crumbs, or

recipitated and washed cellulose xanthate in flocculent condition or in the form of continuous ribbon or filament. The cellulose xanthate in any one of these forms is first subjected to dehydration, say under a vacuum of about 28'inches and at 20 to 30 0., until, a bone-dry product has been produced. The dry product is then ground to fine particle size, say until the particles pass through a 200-mesh sieve, as by passin mill preferably maintained under vacuum conditions or in a dry atmosphere to prevent decomposition of the xanthate during the grinding operation. The dry xanthate power is then preserved in hermetically sealed containers or is treated with a solution of water-re ellent material in an organic solvent suc for example, as ether oralcohol.

For instance, 1t may be intimately mixed with a solution of stearlc ac1d, or theglycerides of stearic, palmitic, or oleic acid'until the particles have been uniformly 'wetted, the soluhave a'coating of, I

tion being of a strength to say, about 1% .by weight'of water-repellent materials on the particles. The resulting ressed free of excess solution anddried un er vacuum and low-temperature conditions. A cellulose xanthate thus stabilized may be kept for months without spoiling. It may be readily dissolved in caustic soda solution to produce a solution suitable for the manufacture of artificial silk and films, or for use in the sizing of textiles or the like. The present invention thus makes possible the production of xanthate where the necessary raw materials are available at low cost and other conditions favorable, and the selling and shipping of the stabilized product to rayon or textile plants so situated as to be unable to produce cellulose xanthate economically, :or to small users who find it more advantageous to buy the xanthate than to prepare it themselves.

Having thus discussed certain embodiments of this invention, it should be evident a raw material such as theor through a ball 7 andr'emoving the solvent.

scope of invention as defined in the append claims.

What we claim is:

1. An article of manufacture consisting of dehydrated cellulose xanthate treated with water-repellent material.

, 2. Anarticle of manufacture consisting of dehydrated cellulose xanthate particles coated :with water-repellent material soluble in a solution of alkali.

3. An article of dehydrated cellulose xanthate freed from impurities and treated with water-repellent material.

4. An article ofmanufacture consisting of dehydrated, precipitated cellulose xanthate treated'with water-repellent material soluble in a solution of alkali.

n 5. .A process which comprises dehydrating cellulose xanthate and then treating with a 'withawater-repellent material.- i

6. A process which comprises dehydrating cellulose xanthate, treating with a solution of water-repellent material in an organic solvent of said material, and removing the ,sol- I vent.

7. A process which comprises dehydrating cellulose xanthate, pulverizing, treating the powder with a solution of water-re ellentma terial in an organic solvent of material,

8. A process wh'ch comprises dehydrating cellulose xanthate, pulverizing, and treating with a water-repellent material.

9. An article of manuf cture consisting of particles uni dehydrated cellulose xanthate formly coated with about 1% water-repellent material. V

10. An article of manufacture consisting of dehydrated cellulose xanthate treated "with fatty acid material. v

11. An article of manufacture consisting of dehydrated cellulose xanthate treated with stearic acid. i

y weight of 12. An article. of manufacture consisting of dehydrated, precipitated cellulose xanthate treated with water-repellent material.

In, testimony whereof we have afiixed our signatures.

' GEORGE A. RICHTER.

PHILIP C. SOHERER, JR.

to those skilled in the art that various changes and modifications might be made therein without departing from the spirit or manufacture consisting of 

